Process for concentrating phosphate ores



June 12, 1956 J. L. HUNTER ETAL 2,750,036

PROCESS FOR CONCENTRATING PHOSPHATE ORES Filed March 16, 1954 2Sheets-Sheet l Phosphate Ore Feed Negative-lori Reagents such as CausticSoda, Fatty Acid and Fuel Oil Conditioning Retarded Flotation (Igegative-lon l. ea ents such as Machine Discharge ccugfic soda,Froth-Product Fatty Acid and High Grade F Oil Phosphate ConcentrateConditioning Froth-Product Scavenger Concentrate Mineral Acid such asSulfuric Acid Agitation (3) Water Rinsing PosLtive-lon Reagents SpentReagentssuc as the Higher SIImes and Water Allphatlc Amines,etc. Towaste l Flotation l4) Silicious Machine Discharge LFroth ProductPhosphate Concentrate T0 was Flnal Hlgh Grode Phosphate ConcentrateINVENTOR S. HARVlE W. BREATHITT,JR Hg BY JOSEPH L.HUNTER mew ATTORN EYJune 12, 1956 J. L. HUNTER El'AL 2,750,036

PROCESS FOR CONCENTRATING PHOSPHATE ORES I Filed March 16, 1954 2Sheets-Sheet 2 Phosphate Ore Feed Negative Ion Reagents such as CausticSoda, Fatty Acid and Fuel Oil conditioning Retarded Flotation (I) LNegative Ion Reagents such as g ggggf' Caustic Soda, Froth Product 9Fatty Acid and Phosphate Concentrate Fuel Oil 1 Cleaner Flotation (5)cndmmng Scavenger Flotation (2) Machine-Dischar e Froth'product Middnngg SillClOUS achine- Finished Concentrate Discharge to Waste Froth-Product Scavenger Concentrate Agitation (3) Water Rinsing Amines,etc. ToWaste Flotation (4) Machine Discharge I Silicious Froth ProductPhosphate Concentrate To waste Final High Grade Phosphate ConcentrateINVENTORa HARVIE W. BREATHITT,JR. BY JOSEPH L. HUNTER ATTORNEY 44 no. 444444v4 vv 44.

United States Patent PROCESS FOR CONCENTRATING PHOSPHATE ORES Joseph L.Hunter, Bartow, and Harvie W. Breathitt, Jr.,

Lakeland, Fla., assignors to Minerals & Chemicals Corporation ofAmerica, a corporation of Maryland Application March 16, 1954, SerialNo. 416,476

1 Claim. (Cl. 209-166) The present invention relates to a new andimproved method of concentrating phosphate minerals from their ores.

The process described and claimed in U. S. Patent No. 2,293,640 to Cragofor concentrating phosphate ores by flotation has attained wideacceptance in the phosphate industry; and, in fact, almost everyphosphate mining operator in the Florida field uses the Crago process inhis plant. Briefly, the Crago process involves the steps of: (1)subjecting the ore to flotation with negative-ion reagents to separate arougher phosphate concentrate from a silica tailing which is discarded,(2) deoiling the rougher concentrate with a mineral acid, and (3)subjecting the deoiled rougher concentrate ot flotation with positiveionreagents to produce a silicious froth-product which goes to waste, and amachine-discharge which is a high grade phosphate concentrate and thefinal product.

While the Crago process is thus being extensively employed in theindustry, we have invented a new and improved method of concentratingphosphate minerals from their ores which has the important advantageover the Crago process of requiring lesser amounts of reagents to effectbetter recovery from a given feed. The reduction in reagent consumptionmeans a lower reagent cost per unit quantity of the feed for our processas compared with that of Crago.

From the following description of our process and the accompanyingdrawings, the advantages and utility of our invention will be clearlyevident to one skilled in the art. It is to be understood, of course,that the drawings merely represent flow sheets of typical embodiments ofour invention and that various modifications can be made withoutdeparting from the spirit and scope of the invention.

Referring at this time particularly to Figure 1 of the drawings,briefly, our novel process comprises four essential steps which aredenoted 1, 2, 3 and 4 thereon. The steps are: (1) subjecting thephosphate ore flotation feed, in an aqueous pulp, to retardednegative-ion froth flotation treatment, thereby producing a high gradefrothproduct and also a machine-discharge of silicious gangue, too richin phosphate to discard: (2) conditioning the machine-discharge withnegative-ion reagents and then subjecting it, in an aqueous pulp, toscavenger flotation, thus obtaining a froth-product with a highinsoluble content, and a tailing, composed largely of silicious gangue,which is, sent to waste; (3) treating the step 2 frothproduct with amineral acid, followed by water rinsing, to kill the flotative efiect ofthe negative-ion reagents present; and (4) subjecting the acid-treatedmaterial from step 3, in an aqeuous pulp, to positive-ion flotation,thereby removing most of the silicious gangue (which is sent to waste)and producing, as the machine-discharge, a high grade phosphateconcentrate. The step 1 froth-product and the step 4 machine-dischargecan be combined to form the final product.

Another embodiment of our invention is shown in Figure 2. Referring toFigure 2 it will be seen that the process shown therein includes thesame 4 essential steps above described, and the additional step 5 ofcleaning the retarded froth-product from step 1, the middlingmachinedischarge being added to the scavenger flotation froth-productand the combined material treated in accordance with steps 3 and 4. Itis to be understood that cleaning step 5 is not essential to our processand may or may not be used, as desired.

The expressions negative-ion flotation (or flotation with negative-ionreagents) and positive-ion flotation, as employed herein, imply the useof cooperating agents, when necessary, along with the negative-ion orpositive-ion collector. Negative-ion and positive-ion collectorsapplicable for the present process are the same as those disclosed inthe Crago patent, above mentioned.

We prefer sulfuric acid for our step 3 deoiling but other mineral acids,or mixtures thereof, may also be used.

By retarded flotation (step 1 of our process) is meant flotationtreatment conducted in such a way that a relatively lightweight and richfroth-product is removed, and consequently, quite a bit of the phosphateaccompanies the machine-discharge; in other words, the recovery, in thefroth-product, of both weight and phosphate has been retarded. There area number of ways to retard phosphate flotation-to name a few: (a) usinglower than normal quantities of flotation reagents, (b) using acid water(preferably water acidified with sulfuric acid) as control water in theflotation ce1ls,.(c) adding a small quantity of acid to the pulp duringconditioning (e. g., to the last conditioner) and (d) maintaining lowpulp levels in the cells during flotation, thereby removing only therich top portion of the froth.

To facilitate the understanding of our invention and to demonstrate thesuperiority of our process over that of Crago, the following examplesare given.

Example I In this example of the use of our process, the step 1retarding was accomplished by the use of lower than normal quantities offlotation reagents.

A 1,000 gm. charge of phosphate flotation feed (cell feed obtained froman actual recovery plant) was conditioned in an aqueous pulp of 70%solids content for two minutes with 0.35 of caustic soda, 2.0 of fueloil and 0.25 of tall oil, all in pounds per ton of dry feed. Theconditioned material was pulped into a 1,000 gm. minerals separationairflow flotation machine and subjected to froth flotation therein,during which a retarded concentrate was removed. The retardedconcentrate was cleaned once, the products being a high grade phosphateconcentrate and a middling.

The machine-discharge from the first (retarded) flotation operation wasconditioned for two minutes in a 70% solids aqueous pulp with 0.1caustic soda, 1.0 fuel oil and 0.15 tall oil, all in pounds per ton oforiginal dry feed. The conditioned machine-discharge was pulped into a1,000 gm. minerals separation airflow flotation cell and subjected tofroth flotation (scavenger flotation) therein, during which a scavengerconcentrate was removed, leaving behind a tailing of silicious ganguewhich was sent to waste. 7

The scavenger concentrate was combined with the middling from thecleaner float and the whole, in a 50% solids aqueous pulp, agitated withsulfuric acid (1.0 lb. of sulfuric acid per ton of original dry feed)for three minutes. The solids were then rinsed twice wtih neutral tapwater to remove acid and spent reagents, pulped into a 500 gm. mineralsseparation airflow flotation machine and there subjected to flotationwith positive-ion reagents. A siliceous froth-product was removed (anddiscarded) leaving a high grade phosphate concentrate as the ma- PercentPercent Percent Percent Pmduct Weight 13. I. L. Insol. m il 1. Feed100.0 28.4 100.0 2. Cleaned retarded concentrate 28.8 74. 5 3. 2 75. 63. Scavenger tailing 61. 2 2. 3 5. 4. Amino machine-discharge. 7.0 74. 52 7 18.4 5. Aminefroth-product an 9.3 1.0 6. Total concentrate (2and 4)35.8 74.5 3.1 9 1.0

To summarize: from ore containing 28.4% B. P. L. there was obtained aphosphate concentrate of 74.5% B. P. L. (and only 3.1% insoluble)content, representing a recovery of 94.0% of the B. P. L. in said .ore.This beneficiation was achieved at a reagent cost (including the H2504),calculated from current prices, of 19 per ton of concentrate. The costper ton of feed amounted to 6.79.

Example 11 This is an example of the use of the Crago process on feedfrom the same sample as that of Example 1.

A 1,000 gm. charge of the said feed was conditioned in an aqueous pulpof 70% solids for two minutes with 0.45 of caustic soda, 3.0 of fuel oiland 0.40 of tall oil, all in pounds per ton of dry feed. The conditionedmaterial was pulped into a 1,000 gm. minerals separation airflowflotation machine and subjected to froth flotation therein, during whicha rougher concentrate (of phosphate values) froth-product was removed,leaving a siliceous tailing behind as the machine-discharge. Thistailing was discarded.

The rougher concentrate was agitated in an aqueous pulp of 50% solidscontent for three minutes, with 2.0 pounds of H2504 per ton of dryoriginal feed. The solids were then rinsed twice with neutral water toremove acid and spent reagents after which they were pulped into a 500gm. minerals separation airflow flotation machine. Positive-ion reagents(0.05 of Armac-T and 0.14 of kerosene, both in pounds per ton of dryoriginal feed) were added to the pulp in the machine and it was thensubjected to froth flotation treatment during which a frothproductcomposed mostly of siliceous gangue was removed, leaving a high gradephosphate concentrate behind as the machine-discharge. The siliceousfroth-product was discarded and the machine-discharge was the finalproduct.

The results achieved by this test are tabulated below.

In this test, a phosphate concentrate of 74.7% B. P. L., representing arecovery of 91.8% was obtained from the feed ore. The reagent cost here(including H2804.) amounted to 24.7 per ton of concentrate or 8.6l perton of feed.

A comparison of Examples I and II shows that the same quantities ofnegative-ion reagents (caustic soda, fuel oil and tall oil) were usedfor each but that considerably more H2SO4, Armac-T and kerosene wererequired for the latter. The two tests resulted in products of aboutequal grade but the Example I recovery was greater than that of ExampleII by 2.4% (94.0% vs. 91.8%). These two factors (differing reagentquantities for equal feed weights and differing recoveries) compoundedto give our new method a reagent cost advantage of 5.7 per ton ofconcentrate over Cragos.

We prefer to accomplish step 1 retardation by the use of lower thannormal amounts of reagents, as in Example I. However, there areadditional ways of doing this (as hereinbefore pointed out), and to showthat our process is not limited to the low reagent method we areincluding herein the results of a test of our procedure in which theretarding was brought about by the use of acid control water. In thisexample, the feed (a different one from that of Examples I and II) wasconditioned with normal quantities of negative-ion reagents and thensubjected to froth-flotation treatment in water containing sulfuric acidin such concentration that its pH was 2.6. The resulting acid-retardedconcentrate was of high enough grade to make a cleaner float unnecessaryand thus the overall test procedure followed that of Figure 1. This testshowed good results: from ore of 31.3% B. P. L. content, a phosphateconcentrate containing 74.3% B. P. L. and only 3.6% insoluble waseffected; the recovery was 95.3%.

We claim:

A method of concentrating phosphate minerals from their ores whichcomprise the following steps: (1) subjecting the ore, in an aqueouspulp, to retarded froth flotation treatment with negative-ion reagentsthus producing a phosphate concentrate froth product and amachine-discharge composed mostly of siliceous gangue but containing aconsiderable quantity of phosphate; (2) subjecting the saidmachine-discharge in an aqueous pulp t0 scavenger flotation treatment toproduce a low grade froth product and a siliceous tailing which can bediscarded; (3) subjecting the scavenger froth product, in an aqueouspulp, to treatment with a mineral acid followed by rinsing with water,thereby effectively removing negative-ion reagents; (4) subjecting theacid-treated and rinsed material, in an aqueous pulp, to froth flotationtreatment with positive-ion reagents, thereby producing a forth productcomposed mostly of siliceous gangue which can be discarded and a residuewhich is a high grade phosphate concentrate; and (5) subjecting thephosphate concentrate froth product from step (1) to cleaner flotationto produce, as part of the final product, a froth product having a lowinsoluble content, and a middling residue which is combined with thestep (2) scavenger froth product prior to the acid treatment step (3).

References Cited in the file of this patent UNITED STATES PATENTS2,661,842 Duke et a1 Dec. 8, 1953

